This invention relates to raise drills and, in particular, to the supporting and guiding structure for raising and lowering the drill head portion of the apparatus. Raise drilling is a term which relates to a technique of boring or reaming large diameter holes which includes drilling a relatively small diameter pilot hole into earth strata until the cutting bit emerges into an open space and then replacing the small cutting bit with a specially-designed large-diameter reamer and cutting the larger hole along the path of the pilot hole by pulling the reamer back toward the drill rig. This technique is well known in the art and many such drill rig apparatuses have been developed.
The subject invention relates to two other applications filed on the same day herewith, namely Ser. No. 38,955, which is now U.S. Pat. No. 4,214,445 and entitled "Hydraulic Circuitry for Raise Drill Apparatus", and Ser. No. 38,753 which is entitled "Chuck and Wrench Assembly for Raise Drill Apparatus".
Most such drill rigs utilize hydraulic thrust cylinders for raising and lowering a drill head which itself is rotated by means of an electric or hydraulic motor. Such apparatuses are relatively heavy and utilize high drive torque for the drill head. Two or more hydraulic thrust cylinders are normally used, one located in a balanced geometry around the drill head, and separate guide columns are provided for guiding the up and down movement of the drill head and associated hardware and resisting reactive torque transmitted from the drill head. These guide columns are in all known cases, provided with structural cross-ties at both the top and bottom of the machine for additional torsional stiffness.
One known prior art drill rig manufactured by the Subterranean Division of Kennametal has a pair of cylinders connected to the machine base and a cross-frame mounted for up and down movement around the outer surface of the cylinders. The pistons are connected to the cross-frame through a pair of open channels located around but not engaging the cylinders, the channels and cylinders both being structurally tied at their upper ends through cross-ties or connecting beams.
It has been found that these types of support structures have added to the weight and cost of raise drills. The existence of structural cross-ties and additional support structures have further required special design considerations to allow accessibility for assembly, maintenance and operation.